Allyson Felix and LaShawn Merritt ran the fastest 400 metres in the world this year as they made the US team for the Rio Olympics at the American trials. World champion Felix shook off an ailing right ankle to win the women's 400m in 49.68 seconds to keep alive her bid for a rare 200-400 metres double at the Aug. 5-21 Olympics. Merritt powered home in 43.97 seconds for the men's 400m victory.